400 is another way to right 4 hundreds
He'll make 7 cuts. If you can't see that that is the answer, draw a diagram.
<span>7 * 5 = ?</span>
Wow, that IS really BRAINLY! I’m so jealous

First we must apply the Quotient rule that states,

This means that our derivative becomes,

Now we need to calculate
and 


From here the new equation looks like,

And that is the final result.
Hope this helps.
r3t40